1. Field of the Invention
This invention relates to a fuel injection system for an internal combustion engine, and in particular, to a fuel injection system of the type in which a fuel injection valve of the fuel swirling type is provided in the intake passage at a position upstream of the intake valve.
2. Description of the Related Art
Fuel injection systems may be classed into two types: in one type of fuel injection system, the atomized fuel from the fuel injection valve assumes the form of a thin, bar-like spray directly impinging on the intake valve. In the other type, the atomized fuel from the fuel injection valve diverges conically, aimed thus at the intake valves. As disclosed, for example, in Japanese Patent Unexamined Publications No. 61-237881 and No. 63-50667, and Japanese Utility Model Unexamined Publications No. 61-140174, No. 62-101065 and No. 61-167474, the conventional fuel injection systems are all concerned with the way in which the injected fuel is directed, particularly the way in which the injection is divided and aimed at the intake valves. In Japanese Utility Model Unexamined Publication No. 61-167474, for example, which discloses a fuel injection system of the former type, the position to be aimed at by the injection and the range allowing aimed injection are specified.
In the former type of fuel injection system, in which the atomized fuel that is in the form of a thin, bar-like spray directly impinges upon the intake valve, however, the atomization is not effected to a satisfactory degree, with the result that the HC content in the exhaust gas is augmented. When starting the engine at low temperature, in particular, the atomization effect by the impinging action is diminished due to the lowered viscosity of the fuel, so that the fuel is allowed to flow into the combustion chamber of the engine as a liquid film, resulting in the starting performance of the engine being deteriorated. In the case of the latter type of fuel injection system, in which the atomized fuel spray from the injection valve conically diverges, on the other hand, no consideration is given to the specific configuration which the atomized fuel is to assume, so that the fuel spray impinges upon the upper and lower walls of the inlet ports immediately in front of the intake valves, resulting in the engine exhibiting a rather poor starting performance and the HC content in the exhaust gas being augmented.